One has described in the French patent No 9212885 belonging to the applicant and published under No 2,697,311 a device for the translatory driving of a part forming a piston in a body by the rotation of a rod extending through the said part which is held against rotary motion in the body.
More precisely, the piston-like part was provided with one or several blades the cutting edge of which was inclined with respect to the longitudinal axis of the rod and which projected sidewise through the opening of the piston-like part extended through by the rod for being caused to bite into the external smooth periphery of this rod so as to incise it helically during its rotation and to thus cause the translational motion of the part forming a piston along the rod during this rotation.
Now it has been found that the fitting of the blade or blades into the small hole of the part forming a piston and through which the rod extends was tricky and sometimes even difficult.
Moreover the part forming a piston had to be made fast in rotation to the body by joints and the making fast in rotation of these two elements sometimes was difficult to be obtained more especially as the piston displacing itself axially in the body was necessarily subjected to a torque resulting from the blade or blades biting into the rod extending centrally through the part forming a piston.